DE10302517A1 - Vehicle speed determination with wheel brake pressure information - Google Patents

Abstract

The present invention describes a method and a device with the aid of which a movement quantity representing the longitudinal movement of a vehicle, such as, for example, a vehicle speed or a vehicle deceleration, can be determined. It is assumed that the vehicle is equipped with a braking system. This can also be an automatic braking system, for example, as is known from the prior art by an anti-lock braking system (ABS) and / or an electronic stabilization program (ESP). Furthermore, it is provided that at least a first and a second wheel state of the wheel are recognized during operation of the brake system, wherein a wheel state can be defined, for example, by the movement behavior of the wheel. The essence of the invention is that the determination of the movement variable in the second wheel state takes place as a function of at least one brake pressure of a wheel brake and a comparison of two vehicle deceleration values determined in different ways in the first wheel state. It is particularly advantageous in the invention that no additional components or components (sensors) are required to determine a variable representing the vehicle speed.

Description

State of technology

The invention relates to a method and a device for determining a vehicle speed in dependence of wheel brake pressure information.

Systems are state of the art known to determine a vehicle speed at which determines the vehicle speed using different parameters becomes. The most common Systems use wheel speed information, for example with automatic braking systems.

So is from the DE 195 27 531 C2 a system is known in which the speed is determined for a four-wheel drive vehicle with a longitudinal acceleration sensor. The acceleration value obtained using the longitudinal acceleration sensor is compared with the acceleration of a suitable (slowest or fastest, depending on the situation) wheel and a decision is made as to whether the extrapolation of the speed with the longitudinal acceleration signal or with the wheel acceleration is used to determine a vehicle reference speed shall be.

Another common method for determining the vehicle speed is to infer a vehicle reference speed by appropriately considering the speed information of the wheels. For example, in the DE 38 33 212 A1 a formation of a reference variable for the vehicle speed outside the brake pressure control is described. An average wheel speed is determined essentially on the basis of the speeds of the two driven wheels.

Furthermore, from the DE 25 58 712 A1 a method is known with the aid of which, using the wheel speeds of a braked vehicle, a reference variable approximating the vehicle speed is obtained and this reference variable is used for determining wheel slip.

A method for determining the vehicle speed in the ABS and ASR case is in the DE 39 09 589 A1 described. In addition to the wheel speeds v _Ri, the braking pressures p _i or the braking torques M _Bi or the driving torques are recorded. The vehicle speed at time k is calculated from the vehicle speed determined at time (k-1), a correction factor that determines the sum of the wheel speed differences (v _Ri (k-1) - v _Ri (measured at times (k-1) and k k)) and the sum of the braking torques M _Bi (k) ∼ p _i (k) determined for the time k.

With the present invention described a method and an apparatus with the aid of which the longitudinal movement representing a vehicle Movement size, like for example a vehicle speed or a vehicle deceleration, can be determined. It is assumed that the vehicle is equipped with a braking system. It can be, for example also an automatic braking system, like an anti-lock braking system (ABS) and / or an electronic stabilization program (ESP) the state of the art is known. It is also provided that that at least a first and a when operating the braking system second wheel state of the wheel is detected, a wheel state defined, for example, by the movement behavior of the wheel can be. The essence of the invention is that the Determination of the movement size in the second Wheel condition depending on both of at least one brake pressure of a wheel brake and at least one two movement variables of the first wheel condition. For example, a longitudinal speed of the vehicle, a vehicle deceleration or other variable representing the movement of the vehicle become. It is particularly advantageous about the invention that no additional components or components (sensors) necessary are to determine a quantity representing the vehicle speed.

Advantageously, during the Operation of the braking system records an operating variable. It can be both by an operating variable of the braking system, as well as a company size of vehicle operation act for example of the wheel. It is particularly advantageous that the detection of the first and second wheel status depending from this recorded company size. As a company size for differentiation one of the first and second wheel states is suitable, for example representing the wheel dynamics Size. So can the wheel deceleration with the size of the farm, the wheel slip and / or the frictional connection between the wheel and the road, the change the speed of rotation of a wheel or the slip behavior of the Rades are recorded.

Advantageously, the first Wheel condition determines at least two movement variables that are different Way, for example by different procedures or regulations, be formed. It is provided that at least one of the determined movement variables in the first Wheel condition depends on the brake pressure. To differentiate from the first movement size can be achieved the second movement quantity, for example depend on a wheel speed quantity representing the wheel speed of a wheel.

A further development of the invention provides that the movement size, in particular while of the first wheel condition is detected in at least two ways. Determining the amount of movement first Kind is dependent at least one wheel speed variable, the represents the wheel speed of a wheel, whereas the movement size second Kind depending at least one brake pressure of a wheel brake. Furthermore In particular, it is provided that after the formation of the movement variable of the first kind a comparison of the movement quantities first and the second type. In an advantageous variant of the invention the vehicle deceleration is recorded as the movement variable.

In a special design The ending is provided for a third vehicle deceleration in the second operating state Kind of capture. This third type of vehicle deceleration will also dependent on formed at least one brake pressure. It is still planned the vehicle speed in the second wheel state depending from vehicle deceleration third type and the comparison of the vehicle deceleration of the first and second type to form in the first wheel state.

The vehicle deceleration is advantageously second and third type in the same predetermined way. there In particular, the vehicle deceleration is second and third Kind depending of at least one brake pressure of a wheel brake and / or a coefficient of friction between the brake pad and brake disc and / or the vehicle mass and / or to detect a design-related wheel parameter.

The determination of the vehicle speed is advantageous in a further embodiment of the invention at regular time intervals and depending from a vehicle speed determined in a previous time interval certainly. This results in a renewed speed determination a change of the previous speed value.

The interpretation is particularly advantageous of the first wheel state as a stability phase and the second wheel state as an instability phase, for example during operation of the braking system during ABS braking. As a rule, the speed of the vehicle based on the speed of the fastest wheel, it can happen that during an instability phase ABS braking the speed of the fastest wheel is very far from the speed the vehicle is removed because the deceleration of the braked wheels is very high and therefore not to be neglected are. This deviation from the actual vehicle speed is advantageously compensated for by the invention.

There are further advantages the following description of exemplary embodiments or from the dependent Claims.

The invention is explained below with reference to the embodiments shown in the drawings. It poses 1 the determination of the vehicle speed is shown schematically in a block diagram. 2 shows in a flowchart the sequence when determining the vehicle speed. The 3a and 3b show schematically the forces applied to the wheels. With the 4 a typical speed curve of a wheel is shown during ABS braking.

embodiment

To determine the vehicle deceleration and thus the vehicle speed from the brake pressures on the wheels, the forces and moments that physically attack the tire are taken into account. With their help, a differential equation for the rotation of a wheel is established. This is generally according to 3a and 3b a swirl set for converting the brake pressure into a deceleration a _{vehicle determined} for a non-driven wheel. The sum of all attacking moments results in a change in the state of motion (acceleration) of the wheel: wheel dω / dt = -F Rollreib r R - F br r S + F tires r R (1)
with Θ _wheel moment of inertia of the wheel
dω / dt angular acceleration of the wheel
F _roller friction _roller friction
F _Br braking force of the brake disc
F _tire tire power (indication of the deceleration of the wheel)
r _R Dynamic wheel radius
r _S Distance of the force application point from the wheel rotation axis of the wheel

The tire force is assumed so that if there is no braking force, the moment from the tire force is in equilibrium with the inertia term (Θ _Rad · dω / dt). A positive tire force therefore leads to a positive acceleration of the wheel. The products (Θ _{Ra d} · dω / dt) and (F _{R oll friction} · r _R ) are neglected, so that the following equation results: 0 = -F B r r S + F tires r R , (2)

With ABS control, the wheel is blocked or an attempt is made to decelerate the vehicle as much as possible with the greatest possible longitudinal force. The wheel brake pressures are set accordingly so that this maximum is reached. Therefore, in this case, the tire force reflects (F _{Reif s),} which is calculated from the braking force (F _Br), the longitudinal deceleration a ^* _Fzg resist. F tires = m veh a veh * (3)

The size m _{vehicle describes} the vehicle mass. From equation 2 we get: F tires = F br r S / r R (4)

For the longitudinal deceleration one obtains from equation 3 and equation 4: a veh * = F br r s / (R R m veh ) (5)

The braking force F _Br between the brake pads (brake caliper) and the brake disc results from the brake pressure p _Br ^* , the commutated brake piston surface A and the coefficient of friction μ _Br between the brake pads and the brake disc. F br = μ br A p B r * (6)

The longitudinal deceleration at a wheel i results from equations 5 and 6 a veh * = (μ br A P br * r s ) / (R R m veh ) (7)

The deceleration a _Fzg ^* represents the deceleration achieved when considering only one brake with brake pressure p _Br ^* . Therefore, the deceleration a _Fzg is now determined by considering all 4 wheel brakes. a veh = (μ br A p br r s ) / (R R m veh ) (8th)

mit vl = vorne links
vr = vorne rechts
hl = hinten links
hr = hinten rechts
i = Laufindex The following applies to the wheel brake pressures p _{Br, i} :

with vl = front left
vr = front right
hl = back left
hr = back right
i = running index

By equation 8 one can Relationship between the wheel brake pressures and the deceleration of the Vehicle are shown.

The block diagram in 1 shows schematically the determination of the vehicle speed during a braking operation. This is done in block 105 by a flag F _B ( 115 ) from the brake system 110 queried whether a braking operation is taking place, a set flag F _B , ie F _B = 1, corresponding to the presence of a braking operation. It does not matter whether the braking process was generated by a braking request made by the driver or by an automatic braking system. Furthermore, this will be in the vehicle sensitive automatic braking system 120 queried for its operating states. In the present exemplary embodiment, an anti-lock braking system (ABS) is queried for whether at least one of the wheels is in a stability phase or in an instability phase. The two phases can be distinguished from one another, for example, by the behavior of the brake pressure applied to the braking force achieved. A stability phase thus represents an area in which an increase in the braking force is possible by increasing the braking pressure, whereas in an instability phase this connection between increasing the braking pressure and the braking force cannot be seen.

The different wheel or operating status is indicated by a flag F _S ( 125 ). A set flag F _S , ie F _S = 1, corresponds to the stability phase. To determine the vehicle speed, it is also necessary to record the wheel brake pressures on the wheel brakes relevant for determining the vehicle speed. Since the reference wheel, which is used to determine the vehicle speed, can change during vehicle operation, all wheel brake pressure variables p _{Br, i} ( 135 ) on the wheel brakes 130 of the vehicle and recorded in the block 105 read. If the vehicle has a weight sensor 140 the current weight of the vehicle m _vehicle ( 145 ) can determine, this information is also in the block 105 read. In addition, however, there is also the possibility of estimating the weight of the vehicle in one block, for example by means of a calculation with the aid of detectable operating parameters of the vehicle, such as vehicle height above the ground, driving behavior during accelerations or wheel contact forces 140 or directly in the block 105 to investigate. With one system 150 , which detects the frictional connection between the brake lining and the brake disc, the frictional connections μ _{Br, i} ( 155 ) of all wheels i are included if the vehicle is equipped with an appropriate system.

In the internal memory 160 the individual wheel parameters or those parameters which are necessary for determining the vehicle speed are stored. For example, as in the 3a and 3b represented by the dynamic wheel radius r _R , the distance of the force application point from the axis of rotation of the wheel r _S and the brake piston _surface A. In addition, however, the vehicle mass m vehicle can also be stored if there is no current value 145 by a weight _sensor 140 or a corresponding weight estimate or calculation can be made available. The data of the memory 160 can be updated by a service technician, for example, if a corresponding change has been made to the vehicle. It is conceivable to change the tires used by changing the tires.

If the vehicle deceleration or vehicle speed has been successfully determined 185 the corresponding value can be displayed 180 be passed on. A usual display for the vehicle speed in vehicles is a speedometer, although other visual and acoustic forms of the speed notification to the driver are also conceivable. In addition to displaying the vehicle speed to the driver, the exact value of the vehicle speed can, however, also be advantageous for some vehicle systems for controlling and regulating the stability of the vehicle. For example, it is conceivable to use the speed in the context of a vehicle dynamics control (FDR) or an adaptive cruise control (ACC). To simplify, these systems are in the block 190 summarized.

The algorithm in 2 shows the flow of a program with which the vehicle speed can be determined as a function of at least one brake pressure of a wheel brake. After the start of the program, a query is made in step 200 as to whether there is a braking operation at the current time. This is done by reading the flag F _B and examining whether it is set (F _B = 1). If this is not the case, the program is ended. However, if a flag F _B ( 115 ) and thus a current braking process is determined, in the next step 210 various parameters are read in, which are necessary for determining the vehicle deceleration or vehicle speed. The values r _S , r _K , A and the wheel pressures p _{B r, i} are thus read in as wheel parameters. In addition, the static friction coefficient μ _i on the wheel i between the wheel and the roadway is present if a corresponding system is present 150 currently read in. Is a weight sensor 140 or if there is a weight estimate or calculation in the vehicle, the associated current weight _value m _vehicle ( 145 ) can also be read. However, if the current values m _vehicle and / or μ _i cannot be recorded individually, a single reading of averaged values of these parameters in step 210 is sufficient from the memory 160 for the further determination of the vehicle deceleration or vehicle speed. In addition to the wheel parameters, the memory 160 a correction factor K is read in, which is available after the first run through a stability phase. This correction factor K represents a factor that is necessary for the calculation of the vehicle _speed if one or more of the parameters m _vehicle , μ _i , A, r _S or r _{R is} not explicitly present or cannot be determined currently.

To recognize the operating state of the brake system, the flag Fs (125) is queried in step 220. This flag F _S ( 125 ) shows, as already mentioned, whether the determined braking process (F _B = 1) is a stability phase or an instability phase. A set flag F _S ( 125 ) that at least one of the wheels, in particular the fastest wheel, is in a stability phase. After determining the first operating state of the braking system, ie a stability phase, the speed v _{0 of} the fastest wheel is determined in step 230. Furthermore, the speed difference Δv is determined in a short period of time Δt. From Δv and Δt we can a Of = Δv / Δt (10)
determine a vehicle deceleration a _Des that corresponds to the actual deceleration of the vehicle. In the subsequent step 240, according to a veh = (μ br A r S p br ) / (r R m F zg ) (11)
determines a vehicle deceleration which is formed as a function of at least one wheel brake pressure of a wheel brake. Since, when determining the vehicle _deceleration a _Fzg according to equation 11, some parameters are necessary which are not present in the presence of corresponding sensors, such as a weight sensor 140 or a system 150 In order to determine the adhesion, which cannot normally be determined currently (μ _Br , m _vehicle , A), a comparison is made in step 250 between the vehicle _deceleration a _Des actually occurred and the vehicle _deceleration a vehicle determined as a function of the wheel brake _pressures K = a Of / a veh (12)
carried out. The correction factor K represents the parameters that are not currently detectable or are explicitly stored in the memory, such as the coefficient of static friction μ _Br , the vehicle mass m _vehicle and the accumulated brake piston area A. The correction factor is stored in the memory for later determination of the vehicle _deceleration or vehicle _speed in the instability _phase 160 stored. However, the parameters mentioned (μ _Br , m _Fzg , A) can currently be determined or as mean _values in the memory 160 stored, the further determination of the vehicle deceleration can be carried out without further correction steps using equation 11.

If no stability phase is determined in step 220 (F _S = 0), the vehicle _deceleration a _Fzg in dependence on the brake pressures p _{Br , i} ( 135 ) determined. The vehicle speed is then determined in step 280 according to v n = v n-1 + a veh K (t n - t n-1 ) (13)
determined as a change in vehicle speed. With v _0, a vehicle speed value from the stability phase is available as the initial value of the speed. Starting from the index start value n = 0, the index n increases by 1 each time the vehicle speed is determined in the instability phase. Equation 13 results in a modification of the vehicle speed taking into account the previous vehicle speed value. The two times t _n and t _n _ ₁ each denote times at which the current vehicle speed or the last vehicle speed was determined. The vehicle speed determined in this way 185 During an instability phase, an appropriate display, for example a speedometer, or suitable vehicle systems can be activated in step 290 190 be forwarded for further processing. After the vehicle speed is displayed, the program begins again at step 200 until the braking process is complete.

To clarify the determination of the vehicle deceleration or vehicle speed, in 4 the time course of ABS braking is shown using a curve a. The essence of the invention is the detection of a stable wheel in area b. Such a wheel stands out from the rest of the wheels in that it has a higher speed and less dynamics. In this phase, the actual deceleration a _{Des of} the vehicle appears in area c. In contrast, a vehicle speed according to d is determined for the averaged deceleration in the instability phase according to equation 11, starting from the previous stability phase. By comparing the actual decelerations in the stability phase with the determined deceleration according to equation 11, one obtains the correction factor K with which the vehicle speed in the range e can be modified.

br

brake disc

R

wheel

F _{roller grater}

Rolling friction force

F _Br

braking force the brake disc

F _tires

tire force (Indication for the delay of the wheel)

r _R

dynamic wheel radius

r _p

opening gap the point of application of force from the wheel's axis of rotation

p _Br

brake pressure

F _B

flag, which indicates a brewing process

F _S

flag, that's a stability phase displays

p _{Br, i}

brake pressure on the bike i

m _Fhz

vehicle mass

a _des

actual delay of the vehicle

a _vehicle ^*

Vehicle deceleration on Wheel i

a _vehicle

averaged vehicle deceleration

μ _i

 Coefficient of static friction between bike and lane on bike i

K

correction factor

110

braking system

120

automatically Brake system (ABS, ESP, etc.)

130

wheel brakes

140

sensor to record the vehicle mass

150

sensor for the adhesion between the wheel and the road

160

internal Storage

180

display the vehicle speed

190

systems, which the driving stability while secure operation

Claims (11)

Method for determining a movement quantity representing the longitudinal movement of a vehicle ( 185 ), the vehicle with a braking system ( 110 ) and during the operation of the brake system ( 110 ) at least - a first and - a second wheel state of at least one wheel is identified, characterized in that the determination of the movement variable ( 185 ) in the second wheel state depending on - at least one brake pressure ( 135 ) a wheel brake ( 130 ) and - at least two differently determined movement variables of the first wheel state. A method according to claim 1, characterized in that during the operation of the braking system ( 110 ) at least one company size ( 125 ) is detected, it being provided that the detection of the first and second wheel status as a function of the operating variable ( 125 ) takes place, it being provided in particular that the company size ( 125 ) represents a variable representing the wheel dynamics, it being provided in particular that the operating variable represents - the wheel deceleration, and / or - the wheel slip, and / or - the frictional connection between the wheel and the road surface. Method according to Claim 1, characterized in that in the first wheel state the determination of at least one movement variable of the first and second type is provided, at least one of the movement variables determined being - a brake pressure ( 135 ) a wheel brake ( 130 ) and / or - a wheel speed variable representing the wheel speed of a wheel. Method according to claim 1 or 3, characterized in that in the first wheel state - depending on at least one wheel speed variable which represents the wheel speed of a wheel, a movement variable of the first type, and - depending on at least one brake pressure ( 135 ) a wheel brake ( 130 ) to detect a movement variable of the second type, it being provided that a comparison of the movement variables of the first and second type is carried out, a vehicle deceleration being provided in particular as the movement variable. A method according to claim 4, characterized in that in the second wheel state depending on at least one brake pressure ( 135 ) a third deceleration of the vehicle is detected, with provision being made for a vehicle speed representing the longitudinal movement of the vehicle ( 185 ) depending on the vehicle deceleration of the third type and the comparison of the vehicle deceleration of the first and second type in the first wheel state. Method according to Claim 5, characterized in that the vehicle deceleration second and third on are recorded in the same predeterminable manner, in particular providing for the vehicle deceleration second and third on depending on at least one brake pressure ( 135 ) a wheel brake ( 130 ), and / or - to determine a coefficient of friction between the brake lining and brake disc, and / or - the vehicle mass, and / or - a design-related wheel parameter. A method according to claim 1 or 5, characterized in that the movement size ( 185 ), in particular the vehicle speed, - is determined at regular time intervals and - as a function of a vehicle speed determined in a previous time interval. Method according to at least one of the preceding claims, characterized characterized that - as first wheel condition a stability phase and - as second wheel condition an instability phase the operation of the Wheel is recognized. Device for determining a movement quantity representing the longitudinal movement of a vehicle ( 185 ), the vehicle with a braking system ( 110 ) and during the operation of the brake system ( 110 ) at least - a first and - a second wheel state of at least one wheel is identified, characterized in that means ( 105 ) to determine the movement size ( 185 ) in the second wheel state depending on - at least one brake pressure ( 135 ) a wheel brake ( 130 ) and - at least two differently determined movement variables of the first wheel state are provided. Device according to claim 9, characterized in that means ( 105 ) are provided which, in the first wheel state - as a function of at least one wheel speed variable which represent the wheel speed of a wheel, a movement variable of the first type, and - as a function of at least one brake pressure ( 135 ) a wheel brake ( 130 ) capture a movement quantity of the second kind, whereby means ( 105 ) are provided, which carry out a comparison of the movement variables of the first and second type, a vehicle deceleration being provided in particular as the movement variable. Device according to claim 4, characterized in that means ( 105 ) are provided, which in the second wheel state depend on at least one brake pressure ( 135 ) detect a third-party vehicle deceleration, with means ( 105 ) are provided, which represent a vehicle speed representing the longitudinal movement of the vehicle ( 185 ) depending on the third-party vehicle deceleration and the comparison form the vehicle deceleration of the first and second type in the first wheel state.